In 1861, Ernest Gaston Joseph Solvay developed the ammonia-soda process for the manufacture of soda ash (anhydrous sodium carbonate) from brine (source of sodium chloride) and limestone (source of calcium carbonate). The process was an improvement over the earlier Leblanc process. The chemistry of Solvay process involves the following chemical equations 1 to 6.a. CaCO3→CaO+CO2  (1)b. CaO+H2O→Ca(OH)2  (2)c. NH3+CO2+H2O→(NH4)HCO3  (3)d. (NH4)HCO3+NaCl→NaHCO3+NH4Cl  (4)e. 2NH4Cl+Ca(OH)2→CaCl2+2NH3+2H2O  (5)f. 2NaHCO3→Na2CO3+CO2+H2O  (6)
The main drawback of the Solvay process is the co-generation of CaCl2 (in the form of distiller waste) which is normally discharged into the sea/river. In this connection, reference may be made to U.S. Pat. No. 6,776,972 by Vohra et al., which discloses the utilization of the distiller waste for the purpose of desulphatation of sea/sub-soil brine which, in turn, results in the production of solar salt of superior quality and reduces the cost of downstream purification of brine. Thus for those soda ash manufacturers who are backward integrated to solar salt production, the above process can be of considerable advantage. No mention is made therein of any value addition of the by-product gypsum obtained in the course of desulphatation which would no doubt be a further motivation to implement the process.
Reference may be made to the Merseberg process wherein gypsum is reacted with ammonia and carbon dioxide to obtain ammonium sulphate solution along with calcium carbonate as precipitate (eq 7). The ammonium sulphate liquor can be separated from the calcium carbonate and thereafter evaporated to recover this important fertilizer. No mention is made in the prior art of any application wherein the calcium carbonate so generated is utilized in the Solvay process as substitute of limestone.CaSO4+2NH3+2H2O+CO2→(NH4)2SO4+CaCO3  (7)
Reference may be made to U.S. Pat. No. 7,041,268 by Ghosh et al. which disclose an integrated process for the recovery of sulphate of potash and magnesia from sea bittern. Gypsum is obtained as a by-product in this process.
Reference is made to the patent application PCT/IN2010/000194 by Ghosh et al. wherein the integrated process for the production of sulphate of potash (SOP), magnesia and ammonium sulphate is disclosed to exploit useful synergies. No reference is made to any integration of the Solvay and Merseberg processes to exploit synergies.
It can be seen from the integrated solar salt-Solvay process (U.S. Pat. No. 6,776,972) and the Merseberg process that there are unexploited synergies between the two in as much as (i) one generates gypsum while the other consumes gypsum, (ii) one generates calcium carbonate and the other consumes calcium carbonate in the form of lime and carbon dioxide, and (iii) both involve similar unit operations in as much as both the reactions use ammonia and carbon dioxide (eqs 3 and 7).
It will be apparent from the process as disclosed in detail below, that integration of the Solvay and Merseberg processes—which is the main object of the invention—is feasible only if there is an additional source of CO2 apart from the CO2 obtained from calcium carbonate. Reference is again made to the Solvay process which involves unit operations at elevated temperatures which would inevitably produce flue gas emissions.
Reference may be made to Wikipedia wherein it is stated that flue gas composition depends on what is being burnt, but that it will usually consist of “mostly nitrogen (typically more than two-thirds) derived from the combustion air, carbon dioxide (CO2) and water vapor as well as excess oxygen (also derived from the combustion air). It further contains a small percentage of pollutants such as particulate matter, carbon monoxide, nitrogen oxides and sulfur oxides”.
Reference is made to U.S. Pat. No. 7,666,234 by Ghosh et al. wherein an improved process for the preparation of biodiesel from triglyceride oils through transesterification is disclosed. The patent discloses the neutralization of spent KOH catalyst in the glycerol layer with acid sources including flue gas.
U.S. patent application 20090191114, (Liu Jian et al., Jul. 30, 2009) describes a method for preparing ammonium bicarbonate with flue gas and device thereof. The method includes quantitatively collecting flue gas with a carbon dioxide concentration of about 8 to 15% (volume), decreasing the temperature of the flue gas to about 50° C., or less, with an air-cooling apparatus, then increasing the pressure of the flue gas and finally allowing the flue gas to react with liquid ammonia to produce ammonium bicarbonate. No mention is made of its application in the Merseberg process.
Reference may be made to a large body of prior art such as U.S. Pat. No. 7,067,456 and PCT application no. PCT/IN2010/000187 (Jasra et al.) which describe different methods of enriching the CO2 in flue gas.